1. Field of the Invention
The present invention relates to a negative resist composition using a polymer suitable for a base resin for a negative resist composition, especially for a chemically amplified negative resist composition, and a patterning process.
2. Description of the Related Art
As LSI progresses toward a high integration and a further acceleration in speed, a miniaturization of a pattern rule rapidly progresses. In particular, the expansion of a flash memory market and the enlargement of a memory capacity lead the finer pattern. As an advanced miniaturization technology, mass production of a 65-nm node device by ArF lithography is achieved. Preparation of mass production of a 45-nm node device by next generation ArF immersion lithography progresses. For a next generation 32-nm node device, immersion lithography by a ultra high NA lens including a liquid having a higher refractive index than water, a high-refractive index lens, and a high-refractive index resist film, extreme ultraviolet (EUV) lithography of 13.5-nm wavelength, a double exposure (double patterning lithography) of ArF lithography, and the like are considered as candidates, and are studied.
In a high energy beam of an extremely short wavelength such as an electron beam (EB) and an X-ray, a light element such as a hydrocarbon used for a resist composition has almost no absorption, and thus a resist composition based on polyhydroxystyrene has been studied.
As the exposure apparatus for mask production, an EB exposure apparatus are used instead of a laser beam exposure apparatus to increase the accuracy of line width. Since a further miniaturization becomes possible by increasing the acceleration voltage of an electron beam gun in the EB exposure apparatus, an acceleration voltage of 10 kV to 30 kV is used, 50 kV becomes a mainstream recently, and an acceleration voltage of 100 kV is also investigated.
As the acceleration voltage increases, a decrease in sensitivity of a resist film becomes a problem. As the acceleration voltage increases, the influence of forward scattering in a resist film becomes reduced. Therefore, the contrast of electron drawing energy is improved to increase resolution and dimensional control. However, electrons pass through the resist film with free draining condition, and therefore the sensitivity of the resist film is decreased. Since a mask exposure machine is used for exposure by direct continuous writing, a decrease in the sensitivity of the resist film leads to a decrease in productivity, and therefore the machine is not preferred. In view of a request for a higher sensitivity, a chemically amplified resist composition is contemplated.
As miniaturization of a pattern of EB lithography for mask production progresses, the thickness of a resist film is decreased to prevent pattern fall due to a high aspect ratio at the time of development. In a case of photolithography, the decrease in the thickness of a resist film contributes greatly to an improvement in a resolution. This is because flattening of a device is promoted by introduction of a CMP and the like. In the mask production, a substrate is flat, and thus the film thickness of the substrate to be processed (e.g., Cr, MoSi, and SiO2) is determined by the light shielding rate and the phase difference control. In order to decrease the thickness of a film, an improvement in dry-etching resistance of a resist is necessary.
It is generally assumed that the carbon density and dry-etching resistance of a resist correlate to each other. Since the EB drawing is not affected by absorption, a resist based on a novolak polymer having excellent etching resistance is developed.
For an improvement in the etching resistance, styrene copolymerization has been first proposed, and indene copolymerization disclosed in Patent Document 1 has been proposed. Further, acenaphthylene copolymerization described in Patent Document 2 is effective in the improvement of etching resistance due to not only high carbon density but also a rigid main chain structure of a cycloolefin structure.
In addition, Patent Document 3 proposes a method for improving the etching resistance by blending a compound containing yttrium, aluminum, iron, titanium, zirconium, or hafnium in an existing resist compound. Examples of a compound containing iron include ferrocene compounds such as ferrocenealdehyde, ferrocenemethanol, ferroceneethanol, ferrocene carboxylic acid, and ferrocene dicarboxylic acid.